1. Field of the Invention
The present invention relates to a method of and an apparatus for manufacturing semiconductor devices or LCDs. More particularly, the present invention relates to exposure apparatus of photolithographic equipment for transferring an image to a substrate, and to an exposure method using the same.
2. Description of the Related Art
A photolithography process is used in the manufacturing of semiconductor devices or LCDs to pattern a resist on a substrate. In the case of semiconductor devices, the substrate is a wafer on which a layer of the resist has been formed. In photolithography, a reticle bearing a mask pattern is illuminated with exposure light of a predetermined wavelength, and the resist is exposed to the light transmitted through the reticle. Accordingly, an image of the mask pattern can be transferred to the wafer. In addition, an exposure apparatus of the photolithography equipment includes a light emitting system for emitting the exposure light that illuminates the reticle, and an optical lens for reducing/projecting the image of the mask pattern of the reticle onto the wafer.
In the meantime, various efforts are being made to improve the resolution of the photolithography process to meet the demand for more highly integrated semiconductor devices. For example, systems and methods have been developed to control the numerical aperture (NA) of the light emitting system of the exposure apparatus.
FIGS. 1 through 3 illustrate a simulation of a photolithography process having a k1 factor of about 0.30, wherein k1=(R×NA)/λ, R is the resolution, NA is the numeral aperture, and λ is the wavelength of the exposure light. More specifically, FIG. 1 is a plan view of the reticle used in the simulated photolithography process, FIG. 2 is a plan view of an aperture plate used to control the NA, and FIG. 3 is a plan view of the pattern 22 transferred to a semiconductor substrate 20 by the photolithography process, i.e. represents the result of the simulation.
Referring to FIG. 1, the reticle 10 has a mask pattern 12 corresponding to the pattern to be transferred to the substrate. In the photolithography process, the mask pattern 12 may be oriented at an acute angle (as shown) with respect to the X-axis of the exposure apparatus or may be oriented parallel to or perpendicular to the X-axis. Also, the direction in which the features of the mask pattern 12 are spaced with the shortest pitch is referred to as the short axis of the mask pattern 12, and the direction in which the features of the mask pattern 12 are spaced with the longest pitch is referred to as the long axis of the mask pattern 12.
The aperture plate 15 has a dipole aperture as illustrated in FIG. 2 and is an NA controller having excellent resolving power with respect to the short axis of the mask pattern 12. However, the aperture plate 15 has low resolving power with respect to the long axis of the mask pattern 12.
Referring to FIG. 3, the pattern 22 transferred to the semiconductor substrate 20 shows that the dipole aperture has excellent resolving power with respect to the short axis direction. That is, the shape of the pattern 22 in the direction of the short axis of the mask pattern 12 can be clearly discriminated. On the contrary, the shape of the pattern 22 in the direction of the long axis of the mask pattern 12 can not be discriminated. That is, whereas features of the mask pattern 12 are spaced from one other along the short axis of the mask pattern 12, the corresponding features of the pattern 22 formed on the substrate 20 are contiguous in the direction of the long axis.
Finally, a double exposure process is one example of a conventional exposure process for controlling the NA. In the double exposure process, a region of a resist on a semiconductor substrate is exposed using a first reticle, and then the same region is subsequently exposed using a reticle having a mask pattern that is different from that of the first mask pattern. Therefore, the reticle is replaced during the double exposure process. Hence, the double exposure process imposes a limit on the throughput of the semiconductor device manufacturing process. Furthermore, the second reticle may not be exactly aligned with the pattern transferred to the resist during the first of the two exposure processes. In this case, a so-called shift of the pattern transferred to the resist occurs. As a result, the contrast of the pattern is poor.